As is well known to persons active in the automotive repair business, the most frequent cause of problems in the cooling systems of automobiles is failure of the thermostat in a closed position. Invariably this causes overheating plus a rise in pressure of the cooling system usually sufficient to rupture either a radiator or heater hose. Whenever this happens, the thermostat must be removed or replaced and the hose replaced or patched before the car can be driven.
Prior art attempts to solve this problem include thermostats specifically designed to "fail safe" by various means to insure that the valve remains in an open position rather than a closed position when the thermostat fails due to corrosion or one reason or another. Examples of such structures may be found in any one of the following prior U.S. Pat. Nos. 2,356,958; 2,842,317; 2,891,730; and 3,498,537. For one reason or another however, such valve structures have not found wide spread commercial acceptance whether due to cost of manufacture or inconsistent operational results or both.
Accordingly, the problem remains to produce a thermostat at reasonable competitive cost with conventional thermostats, which will give comparable service lifetime to conventional thermostats and yet which when it fails, will not result in blockage of coolant circulation with the attendant problems which inevitably follow.